Dynamite improvement in water resistance by coating



Patented Mar. 3, 1942 DYNAMITE IMPROVEMENT IN WATER RESISTANCE BY COATING Robert w. Cairns and William M. Cobb, Jr., wil mington, DeL, assignors to Hercules Powder Company, Wilmington Delaware Del., a corporation of No Drawing. Application December 8, 1938, Serial No. 244,562

20 Claims.

This invention relates to an improved blasting explosive and more particularly to a means of improving the water resistance of non-gelatinous blasting explosives.

The non-gelatinous blasting explosives, commonly called dynamites by the art, normally comprise water soluble inorganic salts, for example, ammonium nitrate or sodium nitrate in admixture with a liquid explosive, for example, nitroglycerine or mixtures thereof with nitroglycol, and wood pulp or other carbonaceous materials.

One disadvantage of the non-gelatinous explosive is the great hygroscopicity and solubility in water of the inorganic nitrate content thereof. During manufacture, storage, and shipment, such dynamites tend to absorb moisture and lose sensitiveness to detonation because of the increased moisture content. Further, when these dynamites are used in wet bore holes, they rapidly absorb water and become inert to detonation.

In the past, attempts have been made to overcome the poor water resistance of dynamites containing water soluble inorganic nitrates by dipping the packed dynamite cartridge into a paraffin bath or the like, but these attempts have met with only partial success. Attempts, also, have been made to improve the water resistance of the dynamites by coating the soluble inorganic nitrate content with water-resistant or water-repellent agents, for example, paramn wax, nitrocellulose, petrolatum, nitrated resin, soaps, sulphurized oils, nitronaphthalenes, nitrotoluenes, sodium silicate, or with various combinations of the above substances.

The coating of the inorganic nitrate crystals with nitronaphthalenes, nitrotoluenes, nitrocellulose or the like is ineffective due to the fact that the nitroglycerine or nitroglycol content of the dynamite dissolves such coatings. The coating of the inorganic nitrate content of the explosive with compounds such as paraffin wax, nitrated resin, petrolatum, sodium silicate, or the like has resulted in a slight improvement in the water resistance of the dynamite, but these coatings have afforded only partial protection against water and moisture.

The object of this invention is to produce a dynamite with improved water resistance. A further object of this invention is to provide a coating agent for the inorganic salt content of the dynamite that will improve the water resistance of the said inorganic salt. A still further object of this invention is to provide a method of coating the inorganic nitrates that are used in dynamites in a manner that will increase the water resistance of the dynamites containing these coated inorganic nitrates. Further ob ects will appear hereinafter.

An improved product in accordance with this invention consists of an inorganic salt containing incorporated'therewith a minor amount of a finely divided metal oxide and having coated thereon a composition containing a resin. The metal oxide used must not be reactive with the inorganic salt with which it is admixed but must be reactive with the resin of the applied coating agent. Further, in accordance with this invention, there has been produced a dynamite product of improved water resistance consisting of a formula that requires the inorganicsalt content of the said dynamite to be of my aforementioned improved type.

In accordance with this invention, an improved coated inorganic salt is prepared by incorporating with an inorganic salt a finely divided metal oxide that is substantially unreactive with the said inorganic salt. After admixture of the inorganic salt and the metal oxide, there is further added a coating agent that contains a resin. The metal oxide which is unreactive with the inorganic salt must be reactive with the resin contained in the coating agent as the presence and reaction of these two substances causes the increase in the water resistance of the inorganic salt being treated. Further, the temperature of the entire process is suitably controlled to provide ready application of th coating agent.

While we prefer to add the metal oxide to the inorganic salt before the additionof the resin coating agent, a favorable result may also be obtained by adding the oxide during or after the addition of the said coating agent.

Thus, our preferred method for improving the water resistance of the inorganic salts used in dynamites includes the addition of a metal oxide within the range of about 0.02% to about 2%, and preferably within the range of about 0.1% to about 0.5% to the inorganic salt, and the addition of a resin coating agent that may include a resin alone, or an admixture including one or more melting point depressants. The amount of coating agent applied is within the range of about 0.1% to about 5.0% and preferably within the range of about 0.5% to about 2.0%. -,The entire mixture is thoroughly incorporated toge her. The temperature of our process is so regulated that the particular coating agent being used may be applied readily to the inorganic salt, and we have found that this temperature will for most coating agents be within the range of about C. to about C.

Among the inorganic salts which have been coated are ammonium nitrate and sodium nitrate, but it will be understood that we contemplate coating any inorganic salt that may be used in dynamite formulation.

The metal oxides which are used in accordance with this invention must be substantially unreactive with the particular inorganic salt that is being coated and must be reactive with the particular resin that is used as the coating agent for the said inorganic salt. Now we have found that among the suitable metal oxides are; for example, the oxides of zinc, mercury, copper, cadmium, and lead. Further, the usable oxides are limited .by the inorganic salt being treated and the resin used as the coating agent, for example, the oxides of the alkali earths react with ammonium nitrate and could not be used in treating this salt, but would be suitable for use with sodium nitrate as there would be no reaction developed. Further examples of inoper-- ative oxides are those oxides of iron, titanium, aluminum, and tin since such oxides do not react "with the resins used a's coating agents. Now, the

,better distribution throughout the salt being treated and provides a product of more uniform water resistance. Therefore, we have used a metal oxide that is at least as fine as 200 mesh although material much finer than this is preferable.

Among the resins which have been used in accordance with this invention are rosin, damar, ester gum, mastic, cumarone-indene resins, glycol-terpinene-maleic anhydride condensation products, gasoline insoluble resins derived from pine wood, and similar resins that are solid at room temperatures, although we prefer to use rosin because of the economical advantage and the equally good results obtained. It is to be noted that these resins are solid at room temperature and further that they are compatible with waxy substances.

Among the melting point depressants which have been used in conjunction with the above resins are wax or wax-like substances such as parafiin, beeswax, hydrogenated castor oil, montan wax, ceresin, etc., but we prefer to select the wax or wax-like substance that upon mixing with a particular resin will afford a mixture that is fluid at temperatures below 110 C. The use of melting point depressants of the wax or waxlike type while not essential, since pure resins may be applied as coatings, is highly desirable because resins alone are difficult to apply safely on oxidizing salts due to the high .temperature required for good spreading.

Where the term coating agent has been used in this specification and claims, it is to be understood to mean a resin, compatible with a waxy substance, alone or such a resin in admixture with a melting point depressant. It will also be understood that although in the specific examples given the coating agent has been applied in a molten or liquid form, we may also apply the coating agent in solution or in apowdered form and obtain favorable results by controlling the temperature of the process to provideeasy and complete distribution and coating.

Having now described in a general way thenature and purpose of this invention, there fol- 20% of which passed 100 mesh and all of which passed a 40 mesh screen. To this granular mass was added one part by weight of powdered zinc oxide and it was thoroughly incorporated with the ammonium nitrate. A molten mixture of 8 parts by weight of "1" Wood rosin and 2 parts i by weight of paraffin wax, heated to about 110 C..

was then poured on the ammonium nitrate-zinc oxide mixture and the entire mixture thoroughly stirred for about 30 minutes. The temperature was maintained at about 100 0., throughout the coating process. The product after being cooled with stirring was screened and was then ready for use in dynamite formulation.

It is essential that the method of coating described hereinbefore includes the addition of a metal oxide to the' inorganic salt bein'g'coate'd;

The presence of the metal oxide is definitely the factor that causes the increased water resistance. Thus it may appear that the cause of the increased water resistance might be attributed to the reaction of the metal oxide with the resin present to form a resinate but it has been found that, although this reaction takes place, it is impossible by directly coating an inorganic salt with a resinate, for example, zinc resinate, to obtain the greatly improved water resistance results that my method of coating provides.

Now to show definitely that the presence of the metal oxide is controlling on the improved water resistance, there were prepared dynamite samples in accordance with the formula of Table 1 in which the ammonium nitrate used was coated in accordance with this invention and for comparison there were also prepared similar dynamites containing ammonium nitrate coated by the same procedure but without the addition of any zinc oxide.

Table I s Per cent Nitroglycerin 12.5 Dinitrotoluene 1.0 Ammonium nitrate (coated) 73.8 Sodium nitrate 5.0 Manioc 2.3 Wood pulp (low grade) 4.7 Chalk 0.7

The comparative water resistances of the dynamites prepared above are shown in Table II.

Table I I Water resistance of' dynamite percent good after 24 hours Coating comgpsitlon immersion 0 cos With 0.1% Without zinc oxide zinc oxide 100% wood rosin u 51 ros n 207 parafiin- 71 50% rosin a paraflin. 61 20% rosin 807 parafliu 44 80% rosin 0 montan wax b 66 80% rosin 20% ceresin n- 61 80% rosin 20% beeswax b 59 507 denier 50% paraflin 61 80% ester gum 20% paraflin 60 80 a mastic 20% parading. 63 80% cumarone-indene resin 20% paraifin c 67 80% glycol-terpinenemaleic anhydride condensation product 20% paraiiin o 31 e 2 hour test.

b 0.2% zinc oxide.

6 6 hour test.

To effect a standard of comparison of thewater resistance of dynamites in which inorganic salts coated in accordance with this invention have been used, with the water resistance of dynamites the open top of the crucible.

coated by the same procedure but without the addition of zinc oxide. the following method of determining water resistance has been used.

A Gooch crucible of about 25 cc. volume was firmly packed with a sample of powder containing the coated salt and covered with a layer of cheesecloth stretched tightly and securely over The crucible was then immersed in water at 65 F. in an inverted position to a depth of about two inches, being suspended by wires through the holes in the crucible bottom. After a predetermined time, the crucible was removed and drained. The dry powder remaining within the crucible was then separated with a knife from the moistened portion and its weight determined and expressed as percentage of the original powder weight.

To show that an improvement in water resistance is noted in dynamite containing other inorganic salts than ammonium nitrate, coated by this process, the following specific example in which sodium nitrate is used and the water resistance results obtaii .ed therefrom are described.

One thousand parts by weight of sodium nitrate, of such a particle size range that all would pass a 20 mesh screen and about 30% passed a 100 mesh screen was coated in a manner similar to that used in coating the ammonium nitrate, described hereinbefore and by using the same proportions of ingredients. That is, the sodium nitrate contained 0.1% of zinc oxide and 1.0% of an 80-20 rosin-paraffin mixture. The coated sodium nitrate of this procedure was used in a dynamite of the formulation given in Table III.

Table III Per cent Nitroglycerin 15.0 Sodium nitrate (coated) 64.3 Manioc 18.2 Wood pulp (low grade) 2.0 Chalk 0.5

The dynamite described above when tested for water resistance showed 79% good powder after 24 hours immersion, whereas a dynamite of similar formulation containing sodium nitrate coated by the same procedure but without the addition of zinc oxide showed 50% good powder after 24 hours immersion in water.

From the specific examples and from the results given, it is obvious that explosives containing salts coated in accordance with this invention show a marked improvement in water resistance. the presence of a metal oxide, such as for example, zinc oxide, will improve any kind of resin coating. However, consideration of practical factors limits our interest to economical oxides, resins, and melting point depressants.

It will be understood that the details and examples given hereinbefore are illustrative only, and in no way limiting on this invention as broadly described hereinbei'ore and in the appended claims,

What we claim and desire to protect by Letters Patent is: a

1. An inorganic nitrate containing a small amount of finely divided metal oxide and coated with a resin solid at room temperatures and having a drop melting point of less than 125 said oxide having substantially no action on said inorganic nitrate, and being reactive with said resin under the conditions of coating.

2. An inorganic nitrate containing a small Furthermore, it will be apparent that amount of finely divided metal oxide and coated with a mixture solid at room temperatures comprising a resin, having a drop melting point of less than about 125 C. and a waxy substance, said oxide having substantially no action on said inorganic nitrate, and being reactive with said resin under the conditions .of coating.

3. Ammonium nitrate containing a small amount of a finely divided metal oxide and coated with a resin solid at room temperatures and having a drop melting point of less than 125 C., said oxide having substantially no action on said nitrate, and being reactive with said resin under the conditions of coating.

4. Ammonium nitrate containing a small amount of finely divided zinc oxide, and coated with a resin solid at room temperatures and having a drop melting point of less than 125 C.

5. Ammonium nitrate containing finely divided zinc oxide within the range of about 0.02% to about 2%, and coated with rosin within the range of about .1% to about 5%.

6. Ammonium nitrate containing a small amount of finely divided metal oxide and coated with a mixture solid at room temperatures comprising a resin, having a drop melting point of less than 125 C. and a waxy substance. said oxide having substantially no action on said nitrate. and being reactive with said resin under conditions of coating.

7. Ammonium nitrate containing a small amount of finely divided zinc oxide and coated with a mixture solid at room temperatures comprising a resin, having a melting point of less than 125 C. and a waxy substance.

8. Ammonium nitrate containing a small amount of finely divided zinc oxide, and coated with a mixture comprising rosin and a waxy substance.

9. Ammonium nitrate containing finely di-- vided zinc oxide within the range of about 02% to about 2%, and coated with about .1% to about 5% of a mixture consisting of about rosin and 20% parafiin.

10. Sodium nitrate containing a small amount of a finely divided metal oxide and coated with a resin solid at room temperatures and having a drop melting point of less than C., said oxide having substantially no action on said nitrate, and being reactive with said resin under the conditions of coating.

11. Sodium nitrate containing a small amount. of finely divided zinc oxide, and coated with a resin solid at room temperatures and having a drop melting point of less than 125 C.

12. Sodium nitrate containing finely divided zinc oxide within the range of about 0.02% to about 2%, and coated with rosin within the range of about .1% to about 5%.

13. Sodium nitrate containing a small amount of finely divided metal oxide and coated with a mixture solid at room temperatures comprising a resin, having a drop melting point of less than 125 C. and a waxy substance, said oxide having substantially no action on said nitrate, and being reactive with said resin under conditions of coating.

14. Sodium nitrate containing a small amount of finely divided zinc oxide and coated with a mixture 'solid at room temperatures comprising a resin, having a drop melting point of less than 125C. and a waxy substance.

15. Sodium nitrate containing a small amount of finely divided zinc oxide, and coated with a mixture comprising rosin and a waxy substance.

nitrate containing flnelv divided zinc aside of about .0296 toabout 2%, and coated with about .1% to about 5% of amixtnre consistingot about 80% and 20% panama.

17. A dynamite including an inorganic nitrate containing a small amount of finely divid d metal oxide and coated with a resin solid at temperatures and having a drop melting point of less than 125 6., said oxide having substantially no action on said inorganic nitrate and being reaclive with aid nsin under the conditions of coat ing. 7 18. A dynamite including an inorganic nitrate containing a small amount of finely divided metal oxide and coated with a mixture solid at room temperatm comprising a resin, having a drop melting point of less than 125 C., and a waxy substance, said oxide having substantially no action on. said inorganic nitrate and being reactive with said resin under the conditions of coat- 1 9. A method comprising the steps of incorporating a small amount of finely divided metal oxide with an inorganic nitrate and treating the resulting admixture at a temperature or between about C. and about 140 C. with a coatin agent that includes'a resin solid at room temperatures and having a drop melting point of less resulting admixture at a temperature betweenabout 90 C. and 140 C. with a coating agent comprising a mixture solid at room temperatures of a resin having a drop melting point of less than 'C., and a waxy substance, said oxide having substantially no action on said inorganic nitrate and being reactive with said resin under the conditions of coating.

- ROBERT W. CAIRNS.

WILLIAM M. COBB, JR. 

